Free piston



Aug. 18, 1953 N. F. BROWN FREE PISTON FOR USE IN EDUCTION PIPES OF APPARATUS FOR RAISING LIQUID IN WELLS Original Filed Feb. '7, 1948 7 Sheets-Sheet l MIR N mm NR [5 A M ATTORNEYS Aug. 18, 1953 N. F. BROWN FREE PISTON FOR USE IN EDUCTION PIPE Re. 23,698 S OF APPARATUS FOR RAISING LIQUID IN WELLS Original Filed Feb. 7, 1948 '7 Sheets-Sheet 2 I ll Aug 18, 1953 N. F. BROWN FREE PISTON FOR USE. IN EDUCTION PIPES OF APPARATUS FOR RAISING LIQUID IN WELLS Original Filed Feb. 7, 1948 '7 Sheets-Sheet 5 Aug. 18, 1953 BROWN Re. 23,698 FREE PISTON FOR USE IN EDUCTION PIPES OF APPARATUS FOR RAISING LIQUID IN WELLS Original Filed Feb. '7, 1948 7 Sheets-Sheet 4 Aug. 18, 1953 N. F. BROWN R 23, 8

FREE PISTON FOR USE IN EDUCTION PIPES OF T Sheets-Sheet 5 APPARATUS FOR RAISING LIQUID IN WELLS Original Filed Feb. '7, 1948 I rill!!! lllllllftf N. F. BROWN FREE PISTON FOR USE IN EDUCTION PIPES OF Aug. 1 8, l 953 APPARATUS FOR RAISING LIQUID I-N WELLS Original Filed Feb. '7, 1948 7 Sheets-Sheet 6 7 Sheets-Sheet '7 F. BROWN ISING LIQUID IN WELLS N. FREE PISTON FOR USE IN EDUCTION PIPES OF APPARATUS FOR RA 7, 1948 #27 Win/727E Aug. 18, 1953 Original Filed Feb.

Reissued Aug. 18,4953

1 EDfiCTI'ON PIPE OF APPKRATUS FOR RAISING LIQUID IN I ils Norman Fraser Brown, London; England; assignor to -NlPFi' Bz'Dfiplacemelit Pump 00. Limited,

ImridemEnglisnd or ma n-oi datea ma 'zs, 1951, Serial I sue 'May 6,828, February 7, 19218, .Application for ,1952, Serial -N0." 285,431. Inv

- re s Gfeat Bl itaifi February 13; 1917 Claims. timers Matter enclosew'iiiha 'appears in the original patent but forms no part of this reissue specification; inatterpfintedin italics indicates the additions made by reissue.

This invention relates to tree pistons for-pumping apparatus for raising naturaIFOiIandother .liquid in Wells whereina'- lug-of liquidis lifted up an oil eduction pipe -to--the--well-- surface-by gas pressure.

When the gas whichlif-ts-gthe'slug, up the pipe is 'in direct c'o'ntactwitlr the base of the liquid slug, some penetration ofthe gas-in-tothe column of liquid will take place tending --t0 produce breakages in the column and a resultant loss in efficiency. To prevent this it is known toprovide a floating plunger adapted-to-be positioned at the lower end of the eduction pipegduring the collection of the slug in the pipe; the plunger being adapted to rise vertically in1;the;-pipe beneath the slug as it is raised -to isolate the'base of the slug from the gas which lifts-it; the plunger falling by gravitydowrr-thei pipevwhenthe slug has been delivered'to-thesurface. v I

According to the present;-invention a free piston adapted to travel up and down" in substantially vertical liquideduction-pipeofawell, is provided with means forautomatically-securing it to said pipe when itreaches theijlimit-ofits downward travel and means responsive'toa variation in the pressure or pressures of fluid; flowing through an orifice-for effecti-ng -the release of the holding means-to permit-the free piston to travel up to the pipe.

The invention also includes afree piston adapted to travel up anddown a. substantially vertical liquid eduction pipe of a well has meansyfor automaticallysecuring it to said pipe when it reaches the limit of --its dow-nward -travel and means, responsive -to-- a variation in;- c lif ferential pressure created across-an eritlee by fiuids flowing therethrough, for eflecting-the release or the holding means to per-Init-the-iree piston to travel up the pipe. W A

The invention further includes-apparatus {or raising liquid 'from wells by -g'lafseous pressure comprising a liquid eduction pipe having a socket at its lower end, and afree" pistonadapted to travel up and down said pipe. andhaving'f neans for automaticallyse'cuifing it: w I the socket when it reaches the'limit of its; wnward mavement, a lower chamber c innectd withth educ tion pipe for collectingliquidfromithe well, means for supplying aseous-pressure t'o'displace liquid from-the loweh; harnb into the eduction pipepast the socket as free, piston secured therein, to forth a sliig of. liciuid' above the free piston, meassidrjautsmaue lyi' leasing the freepi'ston' fr'oii'ith lie ance with a change insandman-pressure created by fluid flowing through an orifice, whereby -2 the piston'is' freed to be lifted up the pipe beneath-the slug by gaseous pressure.

To' enable theinvention' to be fully understood it will now be described with reference to the 5 --accompanying "drawings, in which:

Fig; 1 is a graph showing" a charactris'ticcurve indicating the variations in differential pressure 'across anorifice-through which-fluids are forced to ii'owdiiringa phase of a displacement point)- 'in'g cycle. It'will oeuhderstdo'd that although actual values for pressure differenc'esand' time will vary according to individual conditions and therefore cannot readily be shown in Fig. l. the "shape of'the "curve in' l. is characteristic of all applioatidns-"of the invention.

"Fig. 2 shows in section the sub sur'face equipment-of: one: form of well"'equiprnent'operating the open tube displacement pumping" system such as-described in prior U. S. patent specification 1,930,312 and shows one forrnof socket for receiving a free piston.

* Fig; 3shows in section the above ground apparatus for us'e'w-i'th the equipment shown in Fig. 2.

Fig'.'3a-shows a' section of Fig. 3.

FigaA- and? are sectional views 'of the "upper and lower halves of a free piston according to one embodiment of the invention.

Fig. 4a is "a detail of part of Fig; 4.

Figs. '6 and '7 show details of the catcher mechanism shown in Fig.3.

-FigsJ-8-and 9 show sectional views "of the upper and lower halves respectively of a modified 'form of f -ree. piston.

- Fig-.10 is; an exploded view of the trigger-releasemeehanism shown in Fig. 9.

Fig. 11 is a sectional View of the"upper-half eta further-modifiedform of free piston.

Figs.-;l 2' and- 13 are 'sections' of parts of free vpistens showing still further modifications.

0 Figul' shows-a-suitable form of. subesur-face equipment adapted for using afree piston with a closedtube-displacement pumping system such ee-described in rnyprior U. S; patent specifica- -tion No. ;2,162,418.

Figs. '15': and-l6 -;illustrate sub-surface and surface apparatus particularly for use-with free pistons, as shown :in Fig. 9.

the accompanying drawings, Figs. 2 and n diagrammatic form one form of=app'av r r raising liquid. by the open-tube dis- .pla c'ernentpinnping system, As-shown, the subsurface equipment comprises an outer tube :1 con'r'iected b'ya collar 2 with a large diameter tube s; theldwer slider when is'conn ect ed by-a collar f swanastnriarger diameter ruse s, the interior of which forms the lower or displacement 3 chamber 5 of the apparatus. The bottom end of the tube 6 is closed by a plug 1 having an aperture la and an annular wall 1b forming a recess.

An inner tube or eduction pipe 8 is arranged in the tubes and 3, its lower end being connected with a tubular member 9 adapted to form a housing to receive a free piston to be hereinafter described, the diameter of the member 9 being such as to provide an annular space it between the member 3 and tube 3. The housing member 9 is provided with an annular shoulder having an internal bore slightly less than the bore of the tube 8. At a predetermined distance below the shoulder M, an inwardly extending flange I2 is provided which has a series of axial passages l3. The flange l2 has a similar internal bore to that of the shoulder I A tubular socket portion I4 is provided below the flange l2, and has a flared mouth, one or more axial passages i5, a lateral gas by-pass passage I6, and a closed base having passages H. The bore of the socket member I4 is not uniform but comprises a portion I8 the diameter of which may be slightly greater than a portion 19, but slightly less than the bores in the shoulder I, and flange l2. The collar 4 has a series of axial passages 4a connecting the chamber 5 with the annular space H).

A pipe extends axially into the chamber 5, its upper end extending into a recess in the member 9 through a gland 2|. The pipe 20 is permitted a limited axial movement relative to the member 9, which is limited by an annular collar 22 adapted to cooperate with a shoulder 23. The lower end of the pipe 20 is fitted with a series of sealing rings 24 which engage the walls of the recess lb. The lower end of the pipe 23 is also provided with a series of slots 25, and a non-return valve 25. A pin or the like 26a is provided to limit the upward movement of the valve 26.

A flow guide 21 for liquid is provided surrounding the lower end of the pipe 2|] and comprises a flared upper end 28 having slots 29, a neck 30 and slots 3|. The medial portion of -the flow guide is spaced from the pipe 20 to provide an annular fluid flow passage 32.

The above ground equipment is shown in Fig. 3, and as shown the upper end of the tube I extends through and is supported by a casing head indicated by G and its upper end is connected with a tubing head 33 having a plug 34 from which extends a pipe 35 having slots 36 surrounded by a cage 31. A pipe 38 is connected with the cage and is adapted to receive fluid raised from the well and deliver it to suitable receiving plant, not shown.

Valve means generally indicated by A are provided and comprise a 3-way valve including a spring-loaded exhaust valve A2 having a series of holes A4, Fig. 3a, and a relatively small aperture A3 adapted to be engaged and closed by an auxiliary valve A5 integral with the inlet valve A6. A pilot valve unit B is also provided and comprises a member 39, the upper end of which is adapted to control an exhaust port 40 and the lower end, an inlet port 4| The exhaust port 40 has a greater cross sectional area than the port 4|. In the particular embodiment shown, the member 39 is a floating armature of an electro-magnet and is normally urged by the spring 42 to close the inlet port 4| but is raised to close the exhaust port 4|] when the coil 43 is energised. The coil 43 is adapted to be energised by suitableremote control meansinot of the cylinder 50.

lectable intervals of time.

A diaphragm 44 is provided in a housing C, in the pipe line 38' and has a rod Ca adapted to engage themember 39. The diaphragm is adapted to be actuated by the differential pressure across a restriction 46 created by the flow of liquid through the pipe 33 substantially as described prior U. S. patent application No. 767,947, now Patent No. 2,515,291, dated July 18, 1950. The diaphragm and rod are normally held up by t flspring 45 and a restriction 46 is provided adjacent to the diaphragm, the arrangement being such that the differential pressure created by the gas flow from the pipes 8, 35 ahead of; the liquid rising up the pipe is insuflicient H t depress the diaphragm but the differential pressure across the restriction 45 created by the liquid flowing past it is sufiicient to depress the diaphragm and depress the rod Ca to force the member 39 down in its casing.

At the commencement of a pumping cycle an electrical circuit including the coil 43 is energised to raise the armature member 39 to close the exhaust -port14|l and open the inlet port 4|. Gas at pressure then flows from the pipe Bl, to the pipe B2, valve unit B, pipe B3 to the upper side of a two-step piston A| having atmosphere vents between the steps, to force the piston down and open the valve A6 to supply gas at pressure from pipeB" via pipe 24a to the outer tubing The coil 43 is maintained energised for only a relatively short period but when the coil is no longer energised, the member 39 is maintained in raised position by the pressure existing in the pipe 32- to maintain the exhaust port'40 closedand the port 4| open and the inlet port A6 remains open to supply gas under pressure to the outer tubing the exhaust ports A3, A1 being held closed by the valves A5 and A2 respectively. When the slug of liquid is raised up the well tubing during the later phases of the pumping cycle, and flows over the diaphragm 44, the differential pressure created across the restriction'46 depresses the diaphragm and itsrod" Ca; forces-downthe member 39 to reverse the position of thev'arious valves in units A and B. H

One form of free piston is shown in Figs. 4 and 5 and as shown it comprises a body 47 which is of less diameter than the pipe 8 and is provided with one or more series of wing guides W adapted to centralise the free piston as it ascends on its power stroke and descends on its retum'stroke within the pipe 8. The body 41 is also provided with sealing means in the form of an annular packing member 48 of synthetic rubber or other suitable resilient material. The upper and lower ends of the packing 48 are securedtothe body 41 and its medial portion covers afcylind'rical portion of the body having apertures 49, which connect the inner face of the packer with a cylinder 50 in the body 41. A tube 5| is reciprocably mounted in the body 41 and its upper end is provided with a catcher headHQ The upper portion of the tube 5| carries a piston 52 having a sealing ring 53 making a sliding fluid-tight fit with the wall The tube 5| is closed at the, lower end and houses a spring 54 which is compressed to a partially loaded condition between the closed end of the tube and a cross upper end of the tube 5| and is fixed to the body 41. A rod 56 is secured to the bottom of the tube 5| and extends downwardly through a gland 51 and is provided with a collar 58 normally spaced from the gland 57 and located within a cylindrical portion 59. A piston 60 having a sealing ring 60a is reciprocably mounted in the cylindrical portion 59a and is normally urged to engage and raise the collar 58 by a spring 6| whereby the rod 56 and tube 5| are normally held in their uppermost positions as shown in Fig. 4, the spring 6! having a greater upward thrust than the downward thrust of spring 54. An inner sleeve 62 fitted with a sealing ring 63 extends upwardly from a shoulder 64 on the body of the free piston, and a tube 65 depending from the piston 60 extending into the sleeve 62, makes sliding sealing engagement with the ring 63. The space 66 below the piston 60 is filled with air or gas at low pressure and the collar 58 is formed with slots 58a to ensure that the collar 58 does not completely seal the upper end of the tube 65 when it rests thereon. The space in the cylinder 50 below the piston 52 is filled with liquid such as oil which is adapted to be forced through the apertures 49 to expand the packing 49 radially outwards, when the piston 52 is moved downwardly. Small bore passages 61 lead from the exterior of the body of the free piston to the space 66, the outer end of the passages being covered by a ring of synthetic rubber or other resilient material 68 which nests in an annular groove. This arrangement is shown in the fragmentary detail view of Fig. 4a and is designed to serve as a one-way valve. The arrangement is such that any gas or liquid which may leak into the space 66 past the seals 60a and 63, and raise the pressure in the space 66, will flow out past the ring 68 when the pressure outside the body 41 is at a relatively lower pressure and it will be obvious that any liquid, that may have entered the space 66, naturally settling at the bottom, will be forced out first and followed by any excess gas. A thin flexible sheath 69 formed of synthetic rubber or other suitable material and having axial corrugations is located in the free piston and its opposite ends are secured to axially spaced lips 10 and H. The portion of the free piston body containing the sheath has a series of holes 12 connecting the exterior of the sheath with the exterior of the free piston body and the arrangement is such that the pressure of the well fluids at the holes 12 is transmitted through the sheath to oil or like fluid which fills the interior of the sheath 69, sleeve 62 and cylinders 14, and 59 continuously connected therewith.

A rod 55a depends upon the collar 58 and its lower end carries a piston 13 which reciprocates in a cylinder 14 and is permitted a predetermined upward and downward travel. A tube 15 depends from the piston 13, its end comprising a head 16 having a conically shaped outer surface. A rod ll extends through a hole in the head 16, the upper end of the rod having an enlarged end 18 adapted to engage a shoulder at the lower end of the tube 15 and the lower end of the rod 11 has a head 19 formed with a conical upper and lower portion. The head 19 extends within a slotted portion of the free piston body and is connected thereto by a soft metal shear pin 80 whereby the upward movement of the tube I5 and parts connected thereto is limited, while the shear pin 80 is in place and intact, and upward.

movement is stopped when the head 16 engages the head 18 on the rod 11. Dogs 8|, preferably two in number, are pivctally mounted on pins 82, connected with the body of the free piston, the lower ends of the dogs being normally urged apart by a light spring 83. Each dog comprises a cam face 84 at the upper end and an outwardly projecting dog head 85 at the lower end and an inner cam member 86. Below the slotted portion, the free piston body has a portion 81 of reduced diameter which comprises a cylinder 83 in which is reciprocably mounted a shock absorber piston 89, the rod 90 of which extends through the base of the free piston and is provided with a cap 9! provided with a resilient buffer pad 92 and a light spring 93.

As shown in Figs. 4 and 5 the free piston is positioned in the socket at the lower end of the well tubing, sealing rings 94, 95 engaging the bores I8, I 9 thereby isolating the by-pass passage I5. It will be noted that the free piston is held in the socket by the dog heads 85 on the dogs engaging under the edge of the flange l2 and when in this positiona ring of synthetic rubber or like resilient materia1 96 engages the inner wall of the annular shoulder I l. The outside diameter of the ring 96 is such as to make a fluid-tight fit in the bore of the shoulder II, the upper face of which is flared to facilitateentry of the ring. The ring is provided with one or more axial passages constituting a restricted passage or orifice hereinafter referred to as the orifice Va. The total cross-sectional area of the passage or passages forming the orifice Va is small in comparison with the cross-sectional area of any other passage for the upward flow of well fluids above or below the shoulder ll while the free piston is held in the socket.

During the pump cycle, when liquid from the lower chamber 5, is forced by gaseous pressure up the passage l5 and through the orifice Va, the pressure above the orifice will be lower than the pressure below the orifice, the low pressure being transmitted through the apertures 12 to the flexible sheath 69 and through the sheath to the oil in the space 59, I4 to exert a downward thrust on the pistons and 13. The higher pressure prevailing below the orifice Va is, however, transmitted directly to the underside of the piston 13. The piston 13 is therefore acted upon by the difference in pressure across the orifice Va irrespective of the absolute pressures prevailing.

Liquid from the well enters the chamber 5 past the ball valve 26 during the appropriate phase of the pump cycle and assuming that the chamber 5 has been fllled with more liquid than is required to form a normal length slug of liquid to be raised to the well surface, a cycle of operations commences with the admission of high pressure gas through the valve unit A, pipe 34a to the outer tube I and thence to the upper surface of the liquid in the chamber 5 where the pressure rises to a maximum much sooner than the liquid it can displace from the chamber is in fact displaced. The liquid is displaced from the chamber 5 by the gaseous pressure, through the slots 3| (Fig. 2) up the inside of the flow guide 21, through slots 25 into the pipe 20, the pressure of the liquid in the chamber 5 maintaining the ball valve 263 closed on its seat. The liquid flowing up the pipe 20 flows through the passages 15 and I3 and thence through the orifice Va upwards around the free piston to build up a slug in the l pipe 3 above the free. piston. At the commencement of this first or displacement phase of the cycle of operations when gas pressure in the h oe th p m y 'xi i the rehh i El e h r essure be w 7 13 ei fiiei ei ee h p:

aper tiireslz te the mite icvtf it effcif l and errectg the de the eetionot the spring, Gj'iindl' srrietil' m ge s; h

t 131 W5 1 t l' fl hen f 'l lfidw P81 3? ingfth'ereiea r en thefgas' 'prees the see lingirifng X these pres; r'es is the hydrostatic equivelent of the vertietl e ancefbetw'een thebdttdm' f the seeket and the level S Which lat't ef thechain through th 'p The. pressure bf the gag .flqwin e "15 is'efiectiveipver theid if- '1 areas of ,the bpres lt, l9

' Q'th'e firessure gj the upward 11 Im gummy. the 'k'e he gas the li'quigif in the chamber fm'qm nt ienear'er the lowelflend S and under the free I w 1 feeeete ee nee ey lqqi ie ..l. wi be t'e hat. th head i 1'5 et p ere iee; he c m faces .1 p rm t d a thermq ent oe lew th vemeri rt fieew eeflia cker 49. The movement i 0 er:

' restrietpn A5 and ':the; dih W edeee et it te ionioft e hr e F -F0 pu h...th m mb 39 d wn K130136111 the e ghau st pqrt Ail and, eloserthe port h ees r ne r a te fie tiy t9 ho the nez n 3 9j .-dgwn to keep the port 40 open and pb-rt dl plo eed. I U

l will i be B e e thatiwhe he. d p a m s zeed it will be speced irgm the restriction I QeOrdinghQen unrestricted passage is il z l bl wfp h 19 9 liqui H t i t ieelpeed he exhe-u st port-flfl opened, is paeeeibpve the pie' ton Ai is exhausted and 7 e t vi ei e. .1b he, hre sure beneath. it to cles-ethe inlet valve A5 and shut o ffr thesupply f gaeequg press ureto the outer tube .1 a, The exhv alve A2, is however closed on its seat n lfill A?) has n ufiiQ I hI' to open itegeinst the ges pressure acting on its upperfaee The gee in the pipe], the chamber 5 a t e e im n i the p e19w,., the. fre met 11 now, i egpe nd s, falls in pres sure es the le flfiie n e .fiqi e -;-t e;n e., d flaws emp-el .teql lin ell winei e iqu E t rfi eb ire eivi e lentend deny as at reletiv 1,1 0) pres ur flows backpast valve 2 sui b Q; 3'Q? Li h rvfl fifi bei eiopen d et eiiy hy itS ring when @hfijdQWIU/Vfil'd v Brier .L e; s p e su eie v it s ie m thenthet exerted by thesp ring When thelest of the slug; has been delivered l he-al e; 6 h ir i n: ew e it u p thepipe 35 aipproaehes the end of its upward travel and hits heed. l1 trikesthe bufier of e eeteher assembly. The padefi is at the lpwer end of a tube fl'lwhich is slottegitq aegqmmqdetea cross member 98 of a split cr'osshee d eqf which is rged upwardly by a. spring we whose ends abut the crosshead and carrier. 'Thecrpsshead 99 carries dependin'g' p1'ing blades tel provided at the lower end with jaws I 92 adapted to grip the head H of thefjfree -piston when,desired A rod ")3. exteiicis from the crdsshead. 99 up through the tube 9'! end threhg'h a sealing gland in a tube h'egirij lgggtne "miter end of the rod ,having a ca; Hi .'eag'iable pf being held down by a, clip "16 prvetally' riguilted 'on' the tube head. I M. h 'ma mem .i ts ch h t e h clip isifreed frot en agement with the cap H15 the cr eheariisrai sed by iits spring to pqsition the aws; {ages gh' in Fig 3, b t when the clip hql dsidwn the cap lfii the cros shea q flq is v n the sldt'sl in the tube 91 to cap I and accordingly at the upper. end of its travel the head H of the free piston strikes the buffer pad and its kinetic energy is absorbed mainly by the spring I01 while the rise and fall of the head I85 provides externally visible evidence of the arrival of the free piston. If it is desired to securethe free piston at the top of its travel the clip I06 will be engaged over the cap I85 and accordinglywhen the head H of the free piston strikes the bufier -pad 96 the jaws I02 will catch and hold the head.

The third phase of thepump cycle now com mences and. gas in the pipe line 3 fl, fiows after the liquid to suitable receiving plant. 'The;absolute pressure of the gas in the pipe 8 which acts on the flexible sheath fill now diminishes sufllciently to allow the spring 8| inithe free piston to raise the piston '60 to engage and-raise the collar 58, rods 56, 56a, pistons 52 and F3, tube and the head IE. As a result, thepacking 48 is no longer forcibly expanded and retracts to its normal diameter as shown in Fig. 4 to allow the free piston tofall down the pipe by gravity. The light spring 83 is" also free "to force the lower ends of the dog heads 85 apart ready for automatic re-engag'ement with the flange [2 when the free piston again enters its socket. a V

The fourth phase of the pump cycle now commences as the free piston 'falls'ldownthe pipe As it falls, gas must'flowp'ast the plunger through the restricted space between one or more rastrictor rings such as on the piston body and the'inside wall of the pipe 8, thediameter of the restrictorX being such as to offer a resistance to freeflow'of gas past the free piston as it falls whereby the velocity of the falling free piston may "be pre determin'edand a too rapid descent prevented 1 When the free pistonreaicliessthe end of its downward travel it enters its socket, the dog heads 85 automatically engage under 'the annular flange l2, and the gas by-pass-passage I6 is isolated by the sealing rings 94, 95'before the exhaust valve Az'reopens automatically. -Gas in the tube l during the 4th phase'escape's through the auxiliary valveport'A3'twhich is of such a size that the valve AZTwillnot open before the free piston reaches-the socketin the lower end of the eduction pipep'After the free piston reaches the socket and'some'further reduction of gas pressure has taken place in pipe I, the valve A2 is automatically opened by its spring, and the remaining gas exhausts more past valve A2 than it did through'the' port-A8 and rapidly reduces the pressure in the tube Land lower chamber 5 to permit therefilling of the latter totakeplace.

In the fifth and last phase of the cycle liquid flows by gravity from-the'higher' liquid level outside the chamber, through the passage la past the non-return valve 26 into the chamber 5 ready for a recommencement of the-cycle of operations.

Should any fault occur in the free piston mechanism such as breakage .of the spring 54, damage to the packer 48, loss of-liquid from. the

space 58 or other contingency resulting in the failure of the free piston to riseto the well surface, the head H of the free'pistOnis adapted to beengaged by a catcher or a fishingtoo-l lowered'down the inner tube 8 on a wire line. In this case the'efiect of a pu-ll'on-the'head H by the fishing 'line'will' shear thesoft metal pin 80 to enable'the'reciprocating parts inthe body above that point to be raised relative tothebody of the free piston whereby the head 19 engages the cams 86 to pivot the dogs 8i to withdraw the dog heads from the rib I2 and thereafter an upward pull on the fishing line is transmit ted to the body by the collar 58 which also prevents overtravel of the head 19, to lift it up to the well surface.

The foregoing description assumes that the lower chamber 5 is filled with a quantity of liquid more than sufficient for the formation of a normal slug and that the excess liquid is left behind in the chamber 5 when the free piston and slug are raised up the pipe 8.

Assuming now that the input gas pressure is the same as in the foregoing description but that the lower chamber is only half filled with liquid. The curve shown in Fig; 1 during the first phase of the cycle will be virtually the same, the piston 13 will be raised and the piston 60 lowered, as before. When all the liquid in the chamber 5 is displaced into the pipe 8, the flow of liquid through the orifice Va will be succeeded by a flow of gas and the relative Viscosities of these twofiuids is such that the differential pressure across the orifice created by the gas willbe very small compared with that created by the liquid, and will be quite inadequate to hold the piston, 13, in its upper position. The mechanism will therefore be operated by the spring 54 to release the dogs 8| and expand the packer 48 at a point such as indicated by'Q on the curve of Fig. 1 and phase 2 of the cycle is commenced as soon as all the liquid in the chamber 5 has been displaced into the pipe 8. The gas pressure under the free piston in this case exceeds the equivalent hydrostatic head represented by the combined weight of the slug and free piston, by a greater amount than would be the case if the quantity of liquid displaced from the chamber were greater and the release of the free piston took place at the point P on the curve.

Further, should the gas pressure applied to the upper surface of the liquid collected in the chamber 5 be lower than usual for any reason, the release point P is reached when a shorter than normal slug has been built up above the free piston and a larger proportion of liquid than usual will therefore be left in the chamber 5 when the free piston is released to travel up the pipe 8. The slug and free piston will, however, travel up the pipe at substantially the normal velocity.

Should the gas pressure applied to the upper surface of the liquid in the chamber 5 be higher than usual, and all the liquid in the chamber displaced into the pipe 8 before the point P is reached, the free piston will be released to as cend the pipe when gas flows through the orifice Va after the last of the liquid. In this case a normal length slug will be raised up the pipe 8 at higher than normal velocity.

It will be seen, therefore, that although the amount of liquid displaced into the pipe 8 and the pressure of the gas acting on the upper surface of the liquid in the chamber 5 may vary within reasonable limits, the slug to be raised may be shorter than normal but cannot be longer than the available gas pressure can raise to the well surface.

A modified form of free piston is shown in Figs. 8 and 9. which show the upper and lower halves of the modified free piston engaged in its socket at the bottom of the well tubing. As shown in Figs. 8 and 9 the free piston comprises a body 41a having a cylinder I08 and a sleeve 18a which 11 12 extends into the cylinders: A piston I is recip opposed pairs of blade springs and the detents rocablymounted in the cylinder and has a hollow III-g carridtheieby be! wiing outwardly away pistonrcd I09a having asealinglgland liil which from o e anbth elea'se" the trigger head m. slides over the sleeve 108a. -,A...spr-ing."lii lzhe'hetnts 'a'i 'p'ivbtally mounted on adapted to urge the piston I 09 to its' lower' 'most 5 spaced plates I40 depending from the body porpositions. An annular resilient packer lga sur tion |asa', ;t e platshaving' slots I49 into which rounds a portion of the free piston haring. .aperslide cisssarms isu' ori'the cam I45 which serve tures II2, the opposite ends of the packer being to ceritralisd'th'e cairf'relative'to the blades I4i suitably secured, as'by wire=bindingv Apiston and buttons I42. 3 I-I3-is slidably mounted in thecylinder I which V {The trigger'chamber I35 is only partially filled is filled withcil, or other su-itable liquid[w ich is with oil in this con'stfuctiomleaving an enclosed forced-through the apertures H2 to-eirpand the cushion offgas' to accommodate the displacepacker radially outwardswhenlthe piston I'Ii: is ment ofthe reciprocatingreds' I34, I43.

raised. -A tube I I5 wextendsirom theupperf'aee -The1ow'er endof the rod "I4'3'is connected with of the piston I-I3-th'rough asealing gland. {It} into a piston .I5I re ciproc able in'a' cylinder I52 and the cylinder-I08; the tube-I I5 h'avinglanienllarged provided with a spring I53 adapted to exert a head II'I 'disposedbelow the pistongita; A tube downward pull on it. Apertures I54 are formed I I3 depends from the-underface-ofth piston-I I 13, irt -the-eylinder 152 above the piston I5I and its-bore communicating with -that of the tube 115 passages-"I55 areprovidedatthe lower end of through an'aperturein the piston-[Y3KEhdlpvfr theoylindero {Ilhe'bottom of the free piston has end of the tube H8 is connected-:witli'a flange I {I 5 abufter pad I55; and sealing rings 94a, 95a are supporting a conical head -I ZIl'I A -Spri'ng I2 Iiis provided engaging indifferent diameter bores I8b, provided adapted to exert anupward thruster; IQbof'the-socket to isolate the by-pass gas pasthe piston H3. -Dogs I22 having heads na-a e sage- -;I'6,--substantially as described in relation to pivotally mounted at I22b in a-'slottedportionef 25 Figs; 4"and-5.

the free piston body,- the heads. I 22a being Partsof socket having similar reference nuadapted' to eng-a ge'the shoulder lz -inthe so mera-ls-are-substantially identical with the socket to hold the free --p-iston, b1a"de springs "I114 heme in Fig. 5 but in Fig. 9 the arrangement of the provided to urge the dogs-to engaging position. orifice'is-difierentandinsteadof it being formed The lower end-=of the-tube LIB hasislots 3o by-orifices'inthresilient ring 95 carried by the throughw hich-extends a reciprocating crcs'sha'd freepiston; thisring is dispensed with and the I26 which engages irL-a recess inside the con a orificeis--formed --by-- the --restricted passage Vb head I20.- Asoit-metal shear pin -ll 'liholds both through-which the liquid to'form the slug is the head I20 and-thecrosshead I26 in theii downconstrained'- -to'- flowas -jt is displaced from the most or-normalposition'wThe crosshead com chamber "As' the liquid flows through the renected with aflwire l 28-whichextends up within stricted'orifice vb'a difierential pressure is created thetubes I I8, I I5 and-is clamped-tothe head-iii? across it, the higher-ofupstreampressure actofa rod I3t'iwhich extends-up the sleevel-llga to ing througli-the opemngs- II'inthe base of the thefishinghead-H of the socket.- Ehe cylinder socket and openings I55- in the freepiston, on I08 has holes I3I belowthe. lowermost position 0 the undersi'de?of=-the-piston-l5|; and the lower or of the piston I09 to admit well flu-idsf A resili do'wnst'realm pressure-acting through the holes ent ring-I32'ofsyntheticrubber cr -like material I54 ori the 'uppen side of "this piston. As shown covers series-of apertures I33'to serve-as a'onethe well fluidsract' directly on the opposite sides Way valve tocomp n ny small-leakage bf at the pist'h butifl'desired a sheath or sheaths fluids into the-cylinder" lfl -p -a ie 8 such'as BTmay be providedto'transmit the presing glands substantially as describedw-ith-refersweet thvwell-fiuids-Whil keeping the piston ence to the apertures 6 and-rings Emi Fig.4. from di'rect contact -with them.

Atrigger rod I34 extends downwardly-from the heshown,"the fre piston' is at rest and seflange -I I9 through-a seal- I35-in thebodypart cured inits socket by thedogs' I22. As during I35a,into-a--trigger chamber I35 for-med within th lastpl'iase of the pumpcycle the pressure at therfree pis on-bo y- I The o 134 base trigger t holes I31 'islowand apprbximately the same head I31 the upper face of which is adapted' to as the pi essure"eiiistin'gin the cylinder I08, the engage under detents-l38i pivoted on rains-"I39, spring -II l having a 'greater thrust than the andzurgedinwardlyby blade springs I 40.--Bladc spring I2I foi'cs' down "the-"piston I09 I which springs I 1 secured to- 'e pp e idesf s'theheadll f and in forcing down the each detent I38, each bladebeing fitted with a I button-rl42. The buttonson' the respective-pairs [21 to? the mdsition 'shown iri Fig."8Q The sono bl f nw y end-are l h ly space ical head I20 is below the ends of the dogs I22, apart (-Eig. J10). 1 tlih s I229. bf which 'are'swivelled outwardly rod l 43lextends into the trigger chamber e114; td rig ag' u nder'th'e shoulders through a seal I44, the upper end of the'rcdbei-ng pistdii' fi l'l' 'is in itslo'we'rmost posi connected with -a cammember I45' (Fia 10) kef 48a" is contracted to substantially which: comprises sloping portions I45; I4'I'-(I' ig. terof'thefre "pi'st'oiibody'i The trig- 10) so arranged that'whenthecam I45 is'raised, its upper edgeenters the gaps betweerrthe pairs 0f-buttons--'I4-2 and the blade springs I4I-- separate to-permit the-cam I45 "to pass withouttile I5 2 by" its"sprih g"l53'whereby the blade springs and the detents -I-38-carried thereby "1451's positi new beneath and clear being forced to swing outwardly.- A'fter'thecam o l lTg'l wtiuldffiot'be in the position ould" b'hel'd down at the bottom [45' hasz-passed,-=thebuttonsspringnnoler the' Du'firI-iiha's one of. the pump cycle, liquid sloping-faces I' Il.-=I-Iowever-, if the cam 1-45 is disblsld from the'chamber 5 and flowing up then: moved" downward y the D-p0s d-'= slopi g th'rou'g'mtheorince Vbset'supadifierential'presfaces l'4TWi11 e p s of buttons I42 sure across the"orifice which raises the piston an win tothe comparative vedsewise stiffness I 51 ag'ainst thepull" of the spring I53, and the "spgs m'l;thecam-willta setli c nt 15 erased pa'stthe buttons 142 to the -f5ahdpiston II'S compresses the spring position shown in Fig. 9 Without disengaging the detents I38 from the trigger head I31. As a slug of liquid is built up in a column in the pipe 8 above the free piston, the absolute pressure due to the liquid column rises and this pressure is transmitted through the holes I3I to raise the piston I09 clear of the head II1 on the tube II leaving the piston II3 free to be forced up by its spring I2I as soon as the trigger mechanism is released. As phase I continues the differential pressure across the orifice Vb falls to the point P on the graph of Fig. 1, when the slug above the free piston has reached the appropriate length, or when the difierential pressure falls prematurely from a point such as Q if all the liquid available in the chamber 5 has been displaced and gas follows the last of the liquid through the orifice Vb. In either of these cases the differential pressure acting upwards on the piston I5I is no longer sufficient to hold up the piston which is accordingly forced down by its spring I53. Cam I45 is accordingly pulled down and effects the separation of the detents I35 to free the trigger head I31. The trigger rod is then free to rise and spring I2I raises its piston H3 and with it the head I2Il which engages and swivels the dogs I22 about their pivot I22b to disengage them from the shoulders I23 in the socket. The piston H3 in rising forces the liquid above it, through apertures II2 to act on the inner surface of the packer 48a to expand it radially to make sliding sealing engagement with the wall of the pipe 8 and the free piston then commences to travel up beneath the liquid slug. As previously described, once the free piston leaves its socket gas entering the by-pass passage I6 acts on the cross-sectional area of the free piston to lift it and the slug to the wall surface.

The free piston in this embodiment of the invention may be raised, when necessary by a fishing device adapted to engage the head H. In this embodiment when a fishing line engages the head and an upward pull is applied, the wire I28 is raised and the pin I21 sheared. Upward movement of the cross-head I25 then [raise 5] raises the conical head I20 to engage and move the lower ends of the dogs I 22 apart and thereby disengage the dog heads I22a from the shoulder I23 in the socket without requiring the release of the trigger mechanism. The free piston can then be lifted to the well surface by the fishing line.

A further modified form of free piston is shown in Fig. 11. In this figure only the upper part of the free piston is shown as the mechanism below the dogs I22 is substantially identical with that shown in Figs. 8 and 9. In Fig. 11,

the packer 48b is adapted to be expanded and retracted mechanically, instead of by hydraulic means. The packer 43b, as in the other embodiments, comprises an annular resilient sleeve. The upper end of the packer is secured to the free piston body and its lower end secured to asleeve I56 connected by pins I51 with a collar I58 on a tube I59 extending upwardly of the portion of the free piston body carrying the packer. The apertures for the pins I51 are covered by a seal I51a. The upper end of the tube I59 has a flange I50 engaged by a coil spring I5I tending to urge the tube I59 upwardly from the position shown in Fig. 11. As soon as the trigger mechanism previously described is' released, the tube I59 is raised by the spring IBI, and in rising frees the dogs I22 and lifts the sleeve I56 to apply an axial upwardly directed force to the lower end of the packer 49b causing it to expand radially outwards. A further modification of the free piston according to Fig. 11 is that the absolute pressure piston mechanism of the two embodiments previously described is omitted. In the construction shown in Fig. 11, the arrangement is such that when the free piston arrives at the top of the tube 35 its velocity is such that the head H strikes the buffer pad 96 (Fig. 3) with such momentum that the free piston head H is forced down into the free piston body, the spring I01 being stronger than the spring I6I, in the free piston. The kinetic energy of the upwardly moving piston when it strikes the pad is accordingly utilized to effect the depression of the tube I59, load the spring I6 I and reset the trigger mechanism. The means for raising the free piston by a fishing line is similar to that described with reference to Figs. 8 and 9 except that the upper end of the wire I28a is secured to the head H.

A further modified form of free piston and socket therefor is shown in Fig. 12 and is particularly intended for use in a displacement pumping system where the gas pressure for raising the slug up the well is relatively low and the slug is accordingly raised to the well surface at relatively low velocity. In this arrangement the base i1a of the socket is not provided with axial passages I1 as in Figs. 5 and 9 and the lower end of the free piston has only a single sealing ring IE2 for engaging the socket portion IE3. This socket portion has axial passages I5a and a gas by-pass passage I 6a. Modified shock ab sorber means are also shown in Fig. 12 and comprises a piston I64 and means providing a diminishing fiow passage for oil past it as it is forced upwardly in the cylinder. These means comprise one or more tapered pins I55 extending through a hole I 66 in the piston IE4. Alternatively tapered grooves I61 on the inner wall of the cylinder I63 may be provided as shown in dotted lines. Fig. 13 shows a modified arrangement of orifice for creating the differential pressure to actuate the mechanism in the free piston and as shown, the free piston is provided with a ring X of resilient material similar to the restrictor X of Fig. 4 and formed with a series of annular ridges X2 and the socket portion is formed with a corresponding series of ridges I59. When the free piston is held in the socket the ridges X2 and IE9 are in alignment and an annular orifice V0 is formed between their free ends. The ring X is adapted to serve the dual purpose of acting as means of limiting the velocity of the free piston as it falls down the well tubing against an uprising flow of gas in the pipe 8 and also, when the free piston is in the socket'to cooperate with the ridges I69 to form a restricted orifice for the flow of fluids up past the free piston. It will be understood that the shape of the cooperating parts on the free piston and socket forming the orifice Vc may be varied. As shown in Fig.13-a series of three axially spaced orifices are provided which produce a cumulative drop in pressure in three stages.-

Fig. 13 also shows a modified form of sheath to that shown in Figs. 4 and 5 in that the sheath 69a in Fig. l3 hasradial corrugations instead of the axial corrugations of the sheath 63 of Figs.

4and5 The arrangementshown diagrammatically in Fig. 14 comprises an outer tubing a anda reciprocating inner tubing b such as used in a closed tube" displacement pumping system as describedinpr'ionU.S. PatentNo. 2,162,418. In this arrangemei'ita housing H9 is provided at the lower-end of thereciprocatin-g inner tubing b. When the tubing is is at the bottom of its stroke the housing I19 islocated relative to the other s-u-b surface equipment by a collar ill and contains a cross wijngecl'buifer plate I62. The lower end of the tube b is connected with the displacement'chamber by =api-p'e I13 and the restricted er'iiice'is provided by-a ring I'M having axial passages "Illl. Alternatively the restricted orifice may be provided by an orifice similar to Vb'shown in' 9 or may be formed by cooperat ing parts-on the free piston and socket as described with reference to Fig. 13. It will be noted that in this embodiment of 'the invention the gas bypass I8, and the sealing rings 99, 9 are omitted. The rreepiston may however, embody an expanding packer and mechanism, as describedin any of 'the various" embodiments previously described.

Referring to Figs. 15 and '16 these illustrate an arrangement for use in Wells in which gas pressure in the casing I16 is normally kept high enough to be used effectively in'raising oil slugs. As shown diagrammatically in Fig. 15 the well casing is indicated by I16 and the normal limits of the liquid variations are indicated by ill and H8 respectively. An inner'tube lid is provided having a housingportionto receive a free piston. The housing here shown is similar to that shown in Figs. 8 and 9 and the free piston similar to that shown in Figs. 9 and 11, but in this arrangement lateral gas by-passage E9 is connected with a pipe I82 extending upwardly above the highest expected liquid level in the well to ensure that the gas flowing through the passage IE will be substantially free of liquid. The lower end of the socket hasan extension I93 depending below the lowest' level of liquid in the well casing and is formed with. perforations I84 providing a screened entry for the well liquid. The tubing I19 extends through a well head casing I99 and is provided with a full-bore valve 589. A pipe I91 of a length at least that of the axial length of the free piston extends above the valve I86 and is clamped by a screw ring'IBfl to a valve body generally indicated I89.

As shown in 16 the valve body I99 has an internally extending fiange'IQB separating a lower cavity I9I from a central cavity I92 provided with a fluid flow outlet I93 connected with a delivery line (not shown) leading to suitable fluid receiving plant (not shown). A second flange I94 separates the central cavity I92 from an upper cylinder l 95 and extends upwardly to form a cylinder I96. A reciprocating sleeve is provided having an upper portion I91 and a piston I98 adapted to engage the wall of the cylinder I95. The sleeve is also provided with sealing rings $99 and 299, a slotted portion 29 I, a central sleeve portion 292 and a lower sleeve portion 293 adapted for sliding engagement through the sealing ring 294, and a socket portion 295 adapted to receive the top of the free piston. The top of a free piston which will be substantially as shown in Fig. 11 but is provided with a sealing ring 296 adapted to engage and seal in the socket portion 295. The outside diameter of the lower sleeve 293 is not larger than the bore of the socket 295 and the respective outside diameters of the central and upper sleeve portions 292,19! and slotted portion 29I are smaller than that of the lower sleeve portion 203. One ormore blade springs 20! are provided in the cavity I9I and adapted-to provide resilient-stop means adapted to engage the outer trim of the socket 299. A valve unit iB' is provided which is of the remote controlled"electroemagnetic type butwhich. may be controlled "by known clockwork of pneumatic mechanisms-if desired. The. armature 299 is normally urged into the position shown in Fig. 16 by its spring to "maintain a connection through thevalve'between thecavities 299 and cylinder I and when raisedby energisation of the elec tro-magnet, closes :the passage to the cylinder I95 and connects .theycavity 1299 with atmosphere via the exhaustport'i'ltfl. A small 'hand operated three-way valve ZIsI is provided at the junction of pipes -'2I 2,"2I 3, 2M. 'In normal working position, shown in Fig. 1.6 the valve is positioned to close the pipe'2I2 and connect pipes 2E3, 2;? the latter pipehaving a needle valve or the like 2I5. The valve body has saycap 2 Ifi'fitted with a gland 2H, through which'extends a reciprocating rod 2I8 having'a'head 219, acollar 229 and a buffer head '22I. The rod :2I8 is "normally held in its lowermost position bye spring 222 which when in its extended position has a thrust greater than that of thespring i SI of the free piston (Fig. 11) in the loaded condition. The arrangementxis such "that with the sleeve in its. lowermost position, the :head .H'of the free piston, on reaching the well su-race,, contacts the bufier head 221 when the sealing ringfillfi of the free piston is entered into "the bore of the socket 295. An additional bufilerspring 223 is adapted to contact the end *plug 2116a after the sealing ring 299 has been raised to :enter the cylinder I99, after which further-upward travel of the sleeve is possible by pompressing the springs 223 and 222.

Assuming that title -=well and apparatus are generally as shown and described with reference to Figs. 15,116 with thelevel of liquid at -I "H and a gas pressure of -,say- 751lb./sq. in the well casing above thel-iquidpand assumin'gzthat a free piston substantially as 'shown-i-n-Figs. ll'and 9 but with an orifice" as shown in Fig. 13 is located-in the socket at the bottom of the'pipe H9 and retained by the dogs I22 engagin the annular ring I23. At this stage the sleeve 19! is, in its uppermost position and the slotted portion 29! is located within the cylinder I96 and is isolated therein by the sealing rings 199, 2 99. The cavity I92 and flow line I93 will be at relatively low pressure. The cavities *29 9 and 1I'9I and cylinder I95, the pilot valve B, the tubes I19, I81 and the well casing are all filled with gas at '75 1b./sq. in. and the pilot valve armature 298 is in "the position shown.

With parts in the position described the pilot valve B is actuated to open the exhaust port 2H) and close the passage to the cylinder I95 thereby exhausting the cavity 299 to atmosphere whereupon the sleeve 19'! is thrust downwards by the internal pressure :acting on the piston I98 which has a larger area than that of the seals I99,-290. With thesleeve'in lowered position the slotted portion MI is withdrawn from the cylinder I96 and. gas now flows out of the pipe I19 to the -outlet J93 and as soon as the pressure in the cavities :I9.I, I92 and cylinder I95 and in the valve B reaches a low and -approximately equal pressure, the .valve 298 is returned to its at rest position asshown, once more closin the exhaust port 2 I9 and .opening'the connection between the cylinder I 95 and cavity'299.

Simultaneously there'is a rapid fall in the pres- 17 sure of gas in the pipe I19 above the free piston, and this permits the casing gas pressure acting on the surface I11 of the liquid to displace liquid up the pipe I83 through the orifice passage Vb (Fig. 13) to build up a slug of liquid above the free piston in the pipe I19. As the liquid flows through the orifice Vb a differential pressure across the orifice is set up which has the characteristic of the curve shown in Fig. 1. hydrostatic equivalent of the liquid slug has increased until it is say lb./sq. less than the pressure below the orifice Vb, this representing the vertical height of the point P, above the base line of the curve of Fig. 1, the mechanism in the free piston is actuated as previously described and the dogs are withdrawn, the packing member of the free piston expanded and the 5 lb./sq. in. pressure difference acting beneath the free piston forces it out of its socket Ida and up the pipe I19. Immediately the free piston leaves the socket Ma, the by-pass passage I6 is opened and gas flows down the pipe I82 through the passage I6 and lifts the free piston and slug up the pipe I19. Before the passage I8I is opened the liquid level in the well casing is depressed to approximately the level I18 and the pressure of the liquid acting on the lower end of the orifice Vb is substantially 75 lb./sq. in. minus the hydrostatic equivalent of a liquid column extending from the level I18 to the lower end of the orifice. After the by-pass I6 is opened, however, the gas pressure available through the pipe I82 and applied to lift the free piston, is the full 75 lb./sq. in.

When the slug of liquid reaches the surface it flows through the slots in the portion ZI'II into the outlet I93, preceded by the gas which was above the slug in the pipe I19. Any tendency for the sleeve to rise, due to resistance to fluid flow through it, is checked by the spring blades 291 acting on the outer rim of the socket portion 205.

When the free piston arrives at the surface, its head enters the sleeve and the sealing ring 206 When the,

engages in the socket 205. The liquid slug flowing through the outlet I93 has suflicient momentum to create a temporary low pressure throughout the interior of the sleeve above the free piston and as the pressure beneath the free piston is high, the sleeve is forced upwards overcoming the resilient stop provided by the spring blades 291. The head H of the free piston contacts the buffer head 22I and its further upward movement is resisted by the spring 222. As the upward thrust of the free piston due to the '75 lb. /sq. in. gas pressure beneath it with low pressure above it and the kinetic energy of the moving free piston, is greater than the thrust of the spring IEI in the free piston, the head H will be depressed to force the tube I59 down relatively to the body of the free piston whereby spring I6I will be loaded and held loaded by the detents I38 engagin the head I31 at the lower end of the rod I34, furtherthe packing member 48b is retracted.

If the kinetic energy of the free piston is not all absorbed in loading the spring I6I, the remainder is absorbed by compression of springs 222, 223. Y

The cylinder I95 is now at a pressure lower than the '15 lb./sq. in. in the pipe I19 and the free piston is held up in the socket 205 pneumatically. The pressure in the cylinder I95 commences to be built up by the flow of gas through the choke 2I5 and pipes 2M and M3 and when the pressure in cylinder I95 approaches its higher value the free piston is no longer supported pneumatically and drops out of its socket by gravity and falls down the pipe I19.

After the free piston leaves the socket 205 the sleeve is held in its uppermost position due to the difference between the high pressure inside the sleeve and lower pressure outside it, in the cavity I92, actin on the difference between areas of the sealing rings 200, 294.

At the commencement of the descent of the free piston, the pipe I19 contains a static column ofgas at 75 1b./sq. in. Owing to the efiect of the restrictor rin X, the fall of the free piston causes a drop in the pressure of gas above the free piston. At the end of its descent the free piston enters its socket and re-closes the by-pass passage I6.

When it is desired to remove the free piston, for. examination, repair or replacement, the three-way valve 2I I is turned to shut off the pipe 2 I 4 andestablish a connection between the-cylinder I and central cavity I92 through pipes 2I2, 2 I 3. Accordingly when the free piston arrives at the surface and enters the socket 255 it raises the sleeve. The pneumatic pressure holding up the free piston is now preserved as the flow line is at low pressure and the cylinder I95 is kept at the same low pressure. The arrival of the free piston is indicated by the externally visible upward movement of the head 2I9 and to obtain access to the free piston the valve I86 is closed and the ring I88 unscrewed to permit the removal of the valve body I89 and free piston.

In wells where the gas normally coming out of solution in the well liquid is more than sufficient to raise all the available liquid by the foregoing method, excess gas is taken 01f through the connection I19a; if conditions are such that the natural gas available in the Well is insuflicient in quantity it may be supplemented by gas from a suitable source delivered through the same pipe nae.

If. a well is over-produced and the liquid level falls below the level I18 to the lower end of pipe I83 before a normal slug is built up above the free piston gas will enter the pipe I83 and succeed liquid flowing through the orifice Vb during phase one of the pump cycle before the point P on the curve in Fig. l is reached and the free piston will be released immediately from a point such as Q as previously described.

It will be noted that each of the free pistons shown in the accompanying drawings is provided with one or more sets of wing guides W the object of which is to centralise the free piston as it ascends and descends the pipe. The guides may, however, be also adapted to serve as scrapers for removing wax deposits on the inside of the pipe in which the free piston operates. These wing guides may be made of synthetic rubber or metal.

I claim:

1. [An] In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe, a displacement chamber adjacent to the lower end of said eduction pipe for collecting fluids from the well, conduit means connecting said chamber with the lower end of said pipe, a free piston adapted to travel up and down inside said pipe, means for automatically holding said free piston at the lower end of said pipe when said piston reaches the limit of its downward travel, means for supplying gaseous pressure to displace well fluids from said chamber into said pipe to build up a slug of liquid above said free piston, and orifice through which said well fluids are constrained to flow when they are displaced from said chamber to build up said slug and means responsive to a predetermined change in the differential pressure across said orifice created by the well fluids flowing therethrough to effect the release of said holding means and release the free piston to travel up said eduction pipe, and means for supplying gaseous pressure beneath said free piston to raise it and the slug formed above it up said eduction pipe to the well surface.

2. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe, a displacement chamber adjacent to the lower end of said eduction pipe for collecting fluids from the well, conduit means connecting said chamber with the lower end of said pipe, an abutment adjacent to the lower end of said pipe, a free piston adapted to travel up and down inside said pipe, means on said free piston operable automatically to engage said abutment to secure said free piston to said pipe when said free piston reaches the limit of its downward travel, means for supplying gaseous pressure to displace well fluids from said chamber into said pipe to build up a slug of liquid above said free piston, an orifice through which said well fluids are constrained to now when they are displaced from said chamber to build up said slug, and means responsive to a predetermined change in the differential pressure across said orifice created by the well fluids flowing therethrough to effect the release of said means on said free piston from said abutment to release the said free piston to travel up said eduction pipe, and means for supplying gaseous pressure beneath said free piston to raise it and the slug formed above it up said eduction pipe to the well surface.

3. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe, a free piston adapted to travel up and down inside said pipe, means for automatically holding said free piston at the lower end of said pipe when said piston reaches the limit of its downward travel, means for supplying gaseous pres sure to displace well fluids into said pipe to build up a slug of liquid above said free piston, an orifice through which said well fluids are constrained to flow to build up said slug, and means responsive to a predetermined change in the differential pressure across said orifice created by the well fluids flowing therethrough to effect the release of said holding means and release the free piston to travel up said eduction pipe, and means for supplying gaseous pressure beneath said free piston to raise it and the slug formed above it up said eduction pipe to the well surface.

4. In apparatus for raisingliquid in wells by gaseous pressure,- a vertical liquid eduction pipe, a displacement chamber adjacent to the lower end of said eduction pipe for collecting fluids from the well, conduit means connecting said chamber with the lower end of said pipe, a free piston "dapteii to travel up and down inside said pipe; means for automatically holding said pipe when said piston reaches'the limit of its downward travel, means for supplying gaseous pressure to displace well fluids from said chamber into said pipe to build up a slug of liquid above said ire'e' piston, an orifice through which said well fluids are constrained to flow when they are displaced from said chamber to build up said slug, an auxiliary piston reciprocably mounted in said free piston, and means responsive to a predetermined change in the difierential pressure 7 across said orifice created by the well fluids flowing therethrough to actuate said auxiliary piston to effect the release'cf said holding means and release the free piston to travel up said eduction pipe, and means for supplying gaseous pressure beneath said free piston to raise it and the slug formed above it up said eduction pipe to the well surface.- W i 5. In apparatus for raising liquid in Wells by gaseous pressure,- a vertical liquid eduction pipe, a displacement chamber adjacent to the lower end of said eduction pipe for collecting fluids from the well, condi1it means connecting said chamber with the lower end of said pipe, a free piston adapted to travel up and down inside said pipe, means for automatically holding said free' piston at the lower end or said pipe when said piston reaches the limit of its downward travel, means for supplying gaseous pressure to displace well fluids from said chamber into said pipe to build up a slug of liquid above said free piston, an orifice through which said well fluids are constrained to flow when they are displaced from said chamber to build up said slug, an auxiliary piston reciprocably mounted in said free piston and adapted to be raised within said free piston upon an increase in the difierential pressure created across said orifice by well fluids flowing therethroug'h as said slug is built up in said eduction pipe, and spring means operativeto depress said auxiliary piston upon a reduction in said differential pressure to effect the release of said holding means and release the free piston to tr vel up said eduction pipe, and means for supplying gaseous pressure beneath said free piston to raise it and the slug formed above it up said eduction pipe to the well surface.

6. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe,

a displacement chamber adjacent to the lower end of said eduction pipe for collecting fluids from the well, conduit meansconnecting said chamber with the lower end of said pipe, nee piston adapted to travel up and, down inside said pipe, means for automatically holding said nee piston at the lower or said pipe when said piston reaches the limit of its downward travel, means for supplying gaseous pressure to displace well fluids from said chamber into said pipe to build up a slug [or] of liquid above said free piston, an orifice through which said well fluids are constrained to flow when they are displaced from said chamber to buildup said slug, said free piston comprising a hollow body portion, an auxiliary piston reciprocably mounted in said hollow body portion, spring means for moving saidauxiliary piston in one direction, means for moving said auxiliary piston in the opposite direction against the action of saidspring in accordance with a rise in the differential pressure created,

across said orifice as the well fluids flow therethrough to build up said slug in eduction pipe, and means permitting the actuation of said piston by said spring means upon a reduction in said diflerentialpressureto effectthe release of said holding means andrelease the free piston to travel up said eduction pipe, and means forsupplying gaseous pressure beneath said free piston to raiseit and theslug formed above it up said eduction pipe to the well surface.

7. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eductionpipe, a displacement chamber adjacent to the lower end of said eductionpipe for collecting fluids from the well, conduit means connecting saidchamber with the lower ens of said pipe, a free piston "adapted to travel up and down inside said pipe, a socket at the lower end of said eduction pipe to receive said free piston when it reaches the limit of its downward travel, means for automatically securing said free piston when it enters said socket, means for supplying gaseous pressure to displace well fluids from said chamber into said pipe to build up a slug of liquid above said free piston, an orifice through which said well fluids are constrained to flow when they are displaced from said chamber to build up said slug, and means responsive to a predetermined decrease in the differential pressure across said orifice created by the well fluids flowing therethrough to effect the release of said holding means and release the free piston to travel up said eduction pipe, and means for supplying gaseous pressure beneath said free piston to raise it and the slug formed above it up said eduction pipe to the well surface.

8. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe, a displacement chamber adjacent to the lower end of said eduction pipe for collecting fluids from the well, a free piston adapted to travel up and down inside said pipe, a socket at the lower end of said pipe to receive said free piston when it reaches the limit of its downward travel, abutment means in said pipe adjacent to said socket, means on said free piston automatically engaging said abutment means to secure said free piston in said socket, an axial passage in said socket, means for supplying gaseous pressure to displace well fluids from said chamber through said axial passage into said pipe to build up a slug of liquid above said free piston, and means responsive to a predetermined change in the differential pressure created by the well fluids flowing through said axial passage to eflect the release of said means on the free piston from said abutment means in said pipe and release the free piston to travel up said eduction pipe, and means for supplying gaseous pressure beneath said free piston to raise it and the slug formed above it up said eduction pipe to the well surface.

9. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe, a displacement chamber adjacent to the lower end of said eduction pipe for collecting fluids from the well, conduit means connecting said chamber with the lower end of said pipe, a free piston adapted to travel up and down inside said pipe, a resilient sleeve surrounding part of said free piston, means for automatically holding said free piston at the lower end of said pipe when said piston reaches the limit of its downward travel, means for supplying gaseous pressure to displace well fluids from said chamber into said pipe to build up a slug of liquid above said free piston, an orifice through which said well fluids are constrained to flow when they are displaced from said chamber to build up said slug, and means responsive to a predetermined decrease in the differential pressure across said orifice created by the well fluids flowing therethrough to efiect the release of said holding means and release the free piston to travel up said eduction pipe and to expand said resilient sleeve to make sliding sealing engagement with said pipe, and means for supplying gaseous pressure beneath said free piston to raise it and the slug formed above it up said eduction pipe to the well surface.

10. Apparatus as claimed in claim 9 comprising hydraulically actuated means for effecting the radially outward expansion of said sleeve substantially simultaneously with the release of said:

holding means.

11. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe, a displacement chamber adjacent to the lower end of said eduction pipe for collecting fluids from the well, conduit means connecting said chamber with the lower end of said pipe, a free piston adapted to travel up and down inside said pipe, a resilient sleeve surrounding part of said free piston, means for automatically holding said free piston at the lower end of said pipe when said piston reaches the limit of its downward travel, means for supplying gaseous pressure to displace well fluids from said chamber into said pipe to build up a slug of liquid above said free piston, an orifice through which said well fluids are constrained to flow when they are displaced from said chamber to build up said slug, an auxiliary piston reciprocably mounted in said free piston and means responsive toa predetermined decrease in the differential pressure across said orifice created by the well fluids flowing therethrough to actuate said auxiliary piston to effect the release of said holding means and release the free piston to travel upsaid eduction pipe and to expand said resilient sleeve to make sliding sealing engagement with said pipe and means for supplying gaseous pressure beneath said free,

piston to raise it and the slug formed above it up said eduction pipe to the well surface.-

12. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe, a displacement chamber adjacent to the'lower end of said eduction pipe for collecting fluids from the well, conduit means connecting said chamber with the lower end of said pipe, a free piston adapted to travel up and down inside said pipe, means for automatically holding said :free piston at the lower end of said pipe when said piston reaches the limit of its downward travel, said free piston having a hollow body portion, a rod slidably mounted in said body portion, a spring adapted to actuate said rod, detent means for holding said rod against movement relative to said body portion with the said actuating spring in loaded condition, an auxiliary piston reciprocably mounted in said hollow body portion means connected with said auxiliary piston for releasing said detent means, means for supplying gaseous pressure to displace well fluids from said chamber-into said pipe to build up a slug of liquid above said free piston, an orifice through which said well fluids are constrained to flow when they are displaced from said chamber to build up said slug, and means responsive to a predetermined change in the differential pressure across said orifice created by the well fluids flowing therethrough to actuate said auxiliary piston to release said detent means and free said rod to be actuated by its spring to effeet the release of said holding means and release the free piston to travel up said eduction pipe, and means for supplying gaseous pressure beneath said free piston to raise it and the slug formed above it up said eduction pipe to the well surface.

13. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe, a displacement chamber adjacent to the lower end of said eduction pipe for collecting fluids from the well, conduit means connecting said chamber with the lower end of said pipe, a free piston adapted to travel up and down inside said pipe, means for-automatically holding said free piston at the lower end or said pipe when said piston reaches the limit of its downward travel, said free piston having a hollow body portion, a rod islidably mounted in said body portion, a spring adapted to actuate said red, detent means for holding said rod against movement relative to said body portion with the said actuating spring in loaded condition, an auxiliary piston reciprocably mounted in said hollow body portion, means connected said auxiliary piston for releasing said detent means, a resilient sleeve surrounding part of said hollow body por tion, means for supplying gaseous pressure to displace well fluids from said chamber into said pipe to :build up a slug of liquid above said free piston, an orifice through which said well fluids are constrained to flow when they are displaced from said chamber to build up said Sing, and means responsive to a predetermined change in the differential pressure across said orifice created by the Well fluids flowing therethroug h to actuate said auxiliary piston :to release said detent means and free .said rod to be actuated by its spring to effect ,gthe releaseof said holding means and release the free :"to travel up said eduction pipe rand to eitect the outward radial expansion of said :sleeve :to make sliding sealing engagement with the said ieduction pipe, and means for sup-plying gaseous pressure beneath said free piston to raise and the slug for-med above it up said Jed-notion pipe to the well surface. v

.14. .-In apparatus for raising liquid in wells by gaseous pressure, :a :uerzticazl liquid eduction pipe, a displacement lchambergdajacent to the lower end of said Eduction ipipe for collecting fluids from the :well, roomlui-t HUGS/HS :connecting said chamber the lomer-endcoi said "pipe, a-free piston adapted to lllEBNGl up and down inside said pipe, means for automatically holding said free piston at :the lower end .of said pipe when said piston reaches .the limit :of its downward travel, said lfree cpistnnihayling a ihellowibody por-- tion, ;a ,rod .sl'ida'hly .mmmted in :said body portion, a spring :adaptad Ito actuate saiid rod, detent .meams foriholding said rod against movement relative :to said body ip'ortion with the said actuating .spring in :loaded condition, an auxili-ary piston meciprnca'bly 'mounted in said hollow body rpm tion, mans mmnecited .wvith .sa'id auxiliary piston meleasing said .:detent means, means forsupplytng gaseous zpressure to displace well ifluids afrom :said ichamher into said :pipe to build up iaislug ref diqu'id sabove said tree piston, an orifice through whichsaid well :flu'ids are constrained 1110- flow when :they are displaced from said chamber :tobuild lup zsaid slug, and -means responsive to a predetermined ichange in the a differential pressure :across said orifice -;crea;ted by the well .efluids rfiow'ing itherethrough to actuate said auxiliary pistonrto zrelease said detent means and free :said zrnd 't'o :be -.actuated by its spring to eliect the release :of 'said holding :means I and release the tree "piston to "travel up said eduction pipe, means ion said mod for applying a force axially-of :said sleeve Ito produce aara-dia-l outward expansion thereof, and means for supplying gaseous :[preesune] ,gpmssure ibeneath said free poston terrains it zanditheislug'iormed above it up saidaeduction-zpipeztozthewellsurface.

:15. Apparatus as .elaimed in.=-c'laim 1 2 wherein means areiproyided :for :depressing the said rod relative to lithe ipiston to ire-engage :said dets and de d lsai yao ua ins sprin each time said .free ,pistonarrives ;;at theeupper limit @of its travel up said eduction pipe.

16. Apparatus as'claimed in claim 12 wherein said rod is provided with an extension projecting from the upper end of said free piston, an abutment at the upper end of said pipe cngageable by said extension when said free piston arrives at the upper limit of its travel up said eduction pipe, whereby the kinetic encrg'y'of said upwardly moving piston is utilized to effect the depression of said red by said abutment to load the said actuating spring and effect the re-engagement of the detents to hold said rod in depressed position.

17. A free piston adapted for upward and downward travel inside a vertical liquid eduction pipe of apparatus for raising liquid up said pipe by gaseous pressure, said free piston comprising a hollow body portion, a resilient sleeve surrounding part of said body portion, means on said body portion for automatically securing said free piston at one positio-nin said pipe, means located within said hollow body portion for effecting the release oi said securing means and hydraulically actuated means also located in said hollow body portion for expanding said resilient sleeve radially outwardly.

1 8. n free piston adapted for upward and downward travel inside a vertical liquid eduction pipe of apparatus for-raising liquid up said pipe by gaseous pressure, said free piston comprising a hollow body portion, a resilient sleeve surrounding part of said body portion, means on said body portion for automatically securing said free piston at one position in said pipe, means located within said hollow body portion for effecting the release of said securing means and means also located in said hollo-vv body portion for applying a thrust axially of said resilient sleeve toexpand the same radially outwardly.

18. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe, a displacement chamber adjacent to the lower end of said eduction pipe for collecting fluids from the well, conduit means connecting 'said chaniher with the lower end of said pipe, a free piston adapted to travel up and down inside said pipe, a socket at the lower jend of said ecluot-icn pipe to receive said free piston when it reaches the limit .of its downward travel, means for automatically securing said free piston when it enters said socket, means "for supplying aseous ,pressure to displace well fluids from said chamber into said pipe to build up a slug of liquid above said free piston, an annular resilient member surrounding part of the outersurfaceof saidgfree piston and adapted to make sealing engagement with said pipe when said .free piston is entered into said socket, at least one axial passage in said annular member forming an orifice through whichsaid we'll fluids are constrained to flow when they are displaced from said chamber to build upsaid slug, and means responsiye to a predetermined decrease in-the differential pressure across-saidorific'e created by the well fluids holding means and release the free piston to travel up said eduction pipe, and means for supplying gaseous pressure beneath said free piston to raise it-and the slugifornied above it up said eduction pipe to the Well surface.

20.. In apparatus for raising liquid in wells-by gaseous pressure, a vertical liquid eductionpipe, a displacement chamber adjacent to the --lower end of said eduction pipe for collecting fluids from the well, conduit means connectin .said chamber with-theioyzerend of said pipe, airee p ston adapted to travel up and down inside said pipe, a socket at the lower end of said eduction pipe to receive said free piston when it reaches the limit of its downward travel, means for automatically securing said free piston when it enters said socket, means for supplying gaseous pressure to displace well fluids from said chamber into said pipe to build up a slug of liquid above said free piston, an annular projection on the inner surface of said pipe adjacent to said socket, said annular member and annular projection being adapted to be aligned but spaced radially to form an axial passage therebetween when said free piston is entered into said socket, the said axial passage constituting an orifice through which said well fluids are constrained to flow when they are displaced from said chamber to build up said slug, and means responsive to a predetermined decrease in the differential pressure across said orifice created by the well fluids flowing therethrough to effect the release of said holding means and release the free piston to travel up said eduction pipe, and means for supplying gaseous pressure beneath said free piston to raise it and the slug formed above it up said eduction pipe to the well surface.

21. In apparatus for raising liquid in wells by gaseous pressure, a liquid eduction pipe, a displacement chamber adjacent to the lower end of said pipe for collecting fluids from the well, conduit means connecting said chamber with the lower end of said pipe with said chamber, a free piston adapted to travel up and down inside said pipe, arms pivotally mounted on said free piston, spring means urging said arms outwardly of said free piston, abutments located at the lower end of said pipe for automatic engagement by said arms when said free piston reaches the lower limit of its downward travel in said pipe, means for supplying gaseous pressure to displace well fluids from said chamber into said pipe to build up a slug of liquid above said free piston, a passage through which said well fluids are constrained to flow when displaced from said chamber into said pipe, means responsive to a predetermined reduction in the differential pressure created by said well fluids flowing through said passage, to effect an inward movement of said pivoted arms to disengage them from said abutments and release the piston to travel up said pipe beneath a slug of liquid formed above it in said pipe.

22. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe, a displacement chamber adjacent to the lower end of said eduction pipe for collecting liquid from the well, conduit means connecting said chamber with the lower end of said pipe, a socket located in the lower end of said pipe, a free piston in said socket, means on said free piston holding it in said socket, a passage extending axially within said pipe, means for supplying gaseous pressure to displace well liquid from said chamber through said axial passage into said pipe, a cylinder formed in said free piston, an auxiliary piston reciprocably mounted in said cylinder, a port in said cylinder connecting the space above said auxiliary piston with well fluids at the upper end of said axial passage, a second port connecting the space in said cylinder beneath said piston with well fluids at the lower end of said axial passage, said auxiliary piston being actuated to eifect the release of said free piston from said socket by the differential pressure created by well fluids flowing through said axial passage and acting on opposite sides of said auxiliary piston through said ports, and means for supplying gaseous pressure beneath said free piston to raise it up the said eduction pipe.

23. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe, a displacement chamber adjacent the lower end of said eduction pipe for collecting liquid from the well, conduit means connecting said chamber with the lower end of said pipe, a socket located in the lower end of said pipe, a free piston in said socket, means on said free piston holding it in said socket, a passage extending axially within said pipe, means for supplying gaseous pressure to displace well liquid from said chamber through said axial passage into said eduction pipe, said free piston comprising a hollow body portion, an auxiliary cylinder reciprocably mounted within said body portion, a port in said body portion connecting the space below the underface of said auxiliary piston with the exterior of said body portion adjacent to the lower end of said axial passage, a second port in said cylinder connecting the space above the upper face of said auxiliary piston with the exterior of the body portion adjacent to the upper end of said axial passage, a flexible sheath mounted in said body portion and isolating the inner face of said second mentioned port from the upper face of said auxiliary piston, oil trapped in the space between said sheath and the upper face of said auxiliary piston, and serving to transmit pressure supplied to the outer face of said sheath to the upper face of said auxiliary piston, said auxiliary piston being actuated to effect the release of said free piston from said socket by the differential pressure created by well fluids flowing through said axial passage and acting on opposite sides of said auxiliary piston through said ports, and means for supplying gaseous pressure beneath said free piston to raise it up the said eduction pipe.

24. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe, a displacement chamber adjacent to the lower end of said eduction pipe for collecting fluids from the well, conduit means connecting said chamber with the lower end of said pipe, a free piston adapted to travel up and down inside said pipe, a socket at the lower end of said eduction pipe to receive said free piston when it reaches the limit of its downward travel, means for automatically securing said free piston when it enters said socket, means for supplying gaseous pressure to displace well fluids from said chamber into said pipe to build up a slug of liquid above said free piston, an orifice through which said well fluids are constrained to flow when they are displaced from said chamber to build up said slug, and means responsive to a predetermined decrease in the differential pressure across said orifice created by the well fluids flowing therethrough to effect the release of said holding means and release the free piston to travel up said eduction pipe, a gas by-pass passage in said socket, means on said free piston isolating said gas bypass passage from the interior of said eduction pipe when said free piston is in said socket, and means for supplying gaseous pressure through said by-pass passage when said free piston is released from said socket to raise it and the slug formed above it up said eduction pipe to the well surface.

25. In apparatus for raising liquid in wells by gaseous pressure, a vertical liquid eduction pipe. a free piston adapted to travel up and down in side said pipe, a resilient sleeve surrounding part 

